This updates all source files to use a new standard header for copyright
and license declaration. Notably, copyright no longer includes a date,
and we now use the standard SPDX-License-Identifier header.
This commit was done almost entirely mechanically with perl, and then
some minimal manual fixes.
Updates #6865
Signed-off-by: Will Norris <will@tailscale.com>
They changed a type in their SDK which meant others using the AWS APIs
in their Go programs (with newer AWS modules in their caller go.mod)
and then depending on Tailscale (for e.g. tsnet) then couldn't compile
ipn/store/awsstore.
Thanks to @thisisaaronland for bringing this up.
Fixes#7019
Change-Id: I8d2919183dabd6045a96120bb52940a9bb27193b
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
With a42a594bb3, iOS uses netstack and
hence there are no longer any platforms which use the legacy MagicDNS path. As such, we remove it.
We also normalize the limit for max in-flight DNS queries on iOS (it was 64, now its 256 as per other platforms).
It was 64 for the sake of being cautious about memory, but now we have 50Mb (iOS-15 and greater) instead of 15Mb
so we have the spare headroom.
Signed-off-by: Tom DNetto <tom@tailscale.com>
The macOS client was forgetting to call netstack.Impl.SetLocalBackend.
Change the API so that it can't be started without one, eliminating this
class of bug. Then update all the callers.
Updates #6764
Change-Id: I2b3a4f31fdfd9fdbbbbfe25a42db0c505373562f
Signed-off-by: Claire Wang <claire@tailscale.com>
Co-authored-by: Brad Fitzpatrick <bradfitz@tailscale.com>
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
We've been doing a hard kill of the subprocess, which is only safe as long as
both the cli and gui are not running and the subprocess has had the opportunity
to clean up DNS settings etc. If unattended mode is turned on, this is definitely
unsafe.
I changed babysitProc to close the subprocess's stdin to make it shut down, and
then I plumbed a cancel function into the stdin reader on the subprocess side.
Fixes https://github.com/tailscale/corp/issues/5621
Signed-off-by: Aaron Klotz <aaron@tailscale.com>
This is temporary while we work to upstream performance work in
https://github.com/WireGuard/wireguard-go/pull/64. A replace directive
is less ideal as it breaks dependent code without duplication of the
directive.
Signed-off-by: Jordan Whited <jordan@tailscale.com>
This commit updates the wireguard-go dependency and implements the
necessary changes to the tun.Device and conn.Bind implementations to
support passing vectors of packets in tailscaled. This significantly
improves throughput performance on Linux.
Updates #414
Signed-off-by: Jordan Whited <jordan@tailscale.com>
Signed-off-by: James Tucker <james@tailscale.com>
Co-authored-by: James Tucker <james@tailscale.com>
WinTun is installed lazily by tailscaled while it is running as LocalSystem.
Based upon what we're seeing in bug reports and support requests, removing
WinTun as a lesser user may fail under certain Windows versions, even when that
user is an Administrator.
By adding a user-defined command code to tailscaled, we can ask the service to
do the removal on our behalf while it is still running as LocalSystem.
* The uninstall code is basically the same as it is in corp;
* The command code will be sent as a service control request and is protected by
the SERVICE_USER_DEFINED_CONTROL access right, which requires Administrator.
I'll be adding follow-up patches in corp to engage this functionality.
Updates https://github.com/tailscale/tailscale/issues/6433
Signed-off-by: Aaron Klotz <aaron@tailscale.com>
This handles the case where the inner *os.PathError is wrapped in
another error type, and additionally will redact errors of type
*os.LinkError. Finally, add tests to verify that redaction works.
Signed-off-by: Andrew Dunham <andrew@du.nham.ca>
Change-Id: Ie83424ff6c85cdb29fb48b641330c495107aab7c
renamed from `useNetstack` to `onlyNetstack` which is 1 letter more but
more descriptive because we always have netstack enabled and `useNetstack`
doesn't convey what it is supposed to be used for. e.g. we always use
netstack for Tailscale SSH.
Also renamed shouldWrapNetstack to handleSubnetsInNetstack as it was only used
to configure subnet routing via netstack.
Updates tailscale/corp#8020
Signed-off-by: Maisem Ali <maisem@tailscale.com>
This adds an envknob to make testing async startup more reproducible.
We want the Windows GUI to behave well when wintun is not (or it's
doing its initial slow driver installation), but during testing it's often
too fast to see that it's working. This lets it be slowed down.
Updates #6522
Change-Id: I6ae19f46e270ea679cbaea32a53888efcf2943a7
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
Previously, tstun.Wrapper and magicsock.Conn managed their
own statistics data structure and relied on an external call to
Extract to extract (and reset) the statistics.
This makes it difficult to ensure a maximum size on the statistics
as the caller has no introspection into whether the number
of unique connections is getting too large.
Invert the control flow such that a *connstats.Statistics
is registered with tstun.Wrapper and magicsock.Conn.
Methods on non-nil *connstats.Statistics are called for every packet.
This allows the implementation of connstats.Statistics (in the future)
to better control when it needs to flush to ensure
bounds on maximum sizes.
The value registered into tstun.Wrapper and magicsock.Conn could
be an interface, but that has two performance detriments:
1. Method calls on interface values are more expensive since
they must go through a virtual method dispatch.
2. The implementation would need a sync.Mutex to protect the
statistics value instead of using an atomic.Pointer.
Given that methods on constats.Statistics are called for every packet,
we want reduce the CPU cost on this hot path.
Signed-off-by: Joe Tsai <joetsai@digital-static.net>
Many packages reference the logtail ID types,
but unfortunately pull in the transitive dependencies of logtail.
Fix this problem by putting the log ID types in its own package
with minimal dependencies.
Signed-off-by: Joe Tsai <joetsai@digital-static.net>
tailscaled on Windows had two entirely separate start-up paths for running
as a service vs in the foreground. It's been causing problems for ages.
This unifies the two paths, making them be the same as the path used
for every other platform.
Also, it uses the new async LocalBackend support in ipnserver.Server
so the Server can start serving HTTP immediately, even if tun takes
awhile to come up.
Updates #6535
Change-Id: Icc8c4f96d4887b54a024d7ac15ad11096b5a58cf
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
We use this pattern in a number of places (in this repo and elsewhere)
and I was about to add a fourth to this repo which was crossing the line.
Add this type instead so they're all the same.
Also, we have another Set type (SliceSet, which tracks its keys in
order) in another repo we can move to this package later.
Change-Id: Ibbdcdba5443fae9b6956f63990bdb9e9443cefa9
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
This is step 1 of de-special-casing of Windows and letting the
LocalAPI HTTP server start serving immediately, even while the rest of
the world (notably the Engine and its TUN device) are being created,
which can take a few to dozens of seconds on Windows.
With this change, the ipnserver.New function changes to not take an
Engine and to return immediately, not returning an error, and let its
Run run immediately. If its ServeHTTP is called when it doesn't yet
have a LocalBackend, it returns an error. A TODO in there shows where
a future handler will serve status before an engine is available.
Future changes will:
* delete a bunch of tailscaled_windows.go code and use this new API
* add the ipnserver.Server ServerHTTP handler to await the engine
being available
* use that handler in the Windows GUI client
Updates #6522
Change-Id: Iae94e68c235e850b112a72ea24ad0e0959b568ee
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
We'll eventually remove it entirely, but for now move get it out of ipnserver
where it's distracting and move it to its sole caller.
Updates #6522
Change-Id: I9c6f6a91bf9a8e3c5ea997952b7c08c81723d447
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
It's only used by Windows. No need for it to be in ipn/ipnserver,
which we're trying to trim down.
Change-Id: Idf923ac8b6cdae8b5338ec26c16fb8b5ea548071
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
Follow-up to #6467 and #6506.
LocalBackend knows the server-mode state, so move more auth checking
there, removing some bookkeeping from ipnserver.Server.
Updates #6417
Updates tailscale/corp#8051
Change-Id: Ic5d14a077bf0dccc92a3621bd2646bab2cc5b837
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
This patch removes the crappy, half-backed COM initialization used by `go-ole`
and replaces that with the `StartRuntime` function from `wingoes`, a library I
have started which, among other things, initializes COM properly.
In particular, we should always be initializing COM to use the multithreaded
apartment. Every single OS thread in the process becomes implicitly initialized
as part of the MTA, so we do not need to concern ourselves as to whether or not
any particular OS thread has initialized COM. Furthermore, we no longer need to
lock the OS thread when calling methods on COM interfaces.
Single-threaded apartments are designed solely for working with Win32 threads
that have a message pump; any other use of the STA is invalid.
Fixes https://github.com/tailscale/tailscale/issues/3137
Signed-off-by: Aaron Klotz <aaron@tailscale.com>
Centralize the fake GOOS stuff, start to use it more. To be used more
in the future.
Change-Id: Iabacfbeaf5fca0b53bf4d5dbcdc0367f05a205f9
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
We're trying to gut 90% of the ipnserver package. A lot will get
deleted, some will move to LocalBackend, and a lot is being moved into
this new ipn/ipnauth package which will be leaf-y and testable.
This is a baby step towards moving some stuff to ipnauth.
Update #6417
Updates tailscale/corp#8051
Change-Id: I28bc2126764f46597d92a2d72565009dc6927ee0
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
This uses a go:generate statement to create a bunch of .syso files that
contain a Windows resource file. We check these in since they're less
than 1KiB each, and are only included on Windows.
Fixes#6429
Signed-off-by: Andrew Dunham <andrew@du.nham.ca>
Change-Id: I0512c3c0b2ab9d8d8509cf2037b88b81affcb81f
Run an inotify goroutine and watch if another program takes over
/etc/inotify.conf. Log if so.
For now this only logs. In the future I want to wire it up into the
health system to warn (visible in "tailscale status", etc) about the
situation, with a short URL to more info about how you should really
be using systemd-resolved if you want programs to not fight over your
DNS files on Linux.
Updates #4254 etc etc
Change-Id: I86ad9125717d266d0e3822d4d847d88da6a0daaa
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
Example output:
# Health check:
# - Some peers are advertising routes but --accept-routes is false
Also, move "tailscale status" health checks to the bottom, where they
won't be lost in large netmaps.
Updates #2053
Updates #6266
Change-Id: I5ae76a0cd69a452ce70063875cd7d974bfeb8f1a
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
Leave only the HTTP/auth bits in localapi.
Change-Id: I8e23fb417367f1e0e31483e2982c343ca74086ab
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
This is similar to the golang.org/x/tools/internal/fastwalk I'd
previously written but not recursive and using mem.RO.
The metrics package already had some Linux-specific directory reading
code in it. Move that out to a new general package that can be reused
by portlist too, which helps its scanning of all /proc files:
name old time/op new time/op delta
FindProcessNames-8 2.79ms ± 6% 2.45ms ± 7% -12.11% (p=0.000 n=10+10)
name old alloc/op new alloc/op delta
FindProcessNames-8 62.9kB ± 0% 33.5kB ± 0% -46.76% (p=0.000 n=9+10)
name old allocs/op new allocs/op delta
FindProcessNames-8 2.25k ± 0% 0.38k ± 0% -82.98% (p=0.000 n=9+10)
Change-Id: I75db393032c328f12d95c39f71c9742c375f207a
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
The //go:build syntax was introduced in Go 1.17:
https://go.dev/doc/go1.17#build-lines
gofmt has kept the +build and go:build lines in sync since
then, but enough time has passed. Time to remove them.
Done with:
perl -i -npe 's,^// \+build.*\n,,' $(git grep -l -F '+build')
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
The netlog.Message type is useful to depend on from other packages,
but doing so would transitively cause gvisor and other large packages
to be linked in.
Avoid this problem by moving all network logging types to a single package.
We also update staticcheck to take in:
003d277bcf
Signed-off-by: Joe Tsai <joetsai@digital-static.net>
Turns out using win32 instead of shelling out to child processes is a
bit faster:
name old time/op new time/op delta
GetListIncremental-4 278ms ± 2% 0ms ± 7% -99.93% (p=0.000 n=8+10)
name old alloc/op new alloc/op delta
GetListIncremental-4 238kB ± 0% 9kB ± 0% -96.12% (p=0.000 n=10+8)
name old allocs/op new allocs/op delta
GetListIncremental-4 1.19k ± 0% 0.02k ± 0% -98.49% (p=0.000 n=10+10)
Fixes#3876 (sadly)
Change-Id: I1195ac5de21a8a8b3cdace5871d263e81aa27e91
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
name old time/op new time/op delta
GetList-8 11.2ms ± 5% 11.1ms ± 3% ~ (p=0.661 n=10+9)
name old alloc/op new alloc/op delta
GetList-8 83.3kB ± 1% 67.4kB ± 1% -19.05% (p=0.000 n=10+10)
name old allocs/op new allocs/op delta
GetList-8 2.89k ± 2% 2.19k ± 1% -24.24% (p=0.000 n=10+10)
(real issue is we're calling this code as much as we are, but easy
enough to make it efficient because it'll still need to be called
sometimes in any case)
Updates #5958
Change-Id: I90c20278d73e80315a840aed1397d24faa308d93
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
We removed it in #4806 in favor of the built-in functionality from the
nhooyr.io/websocket package. However, it has an issue with deadlines
that has not been fixed yet (see nhooyr/websocket#350). Temporarily
go back to using a custom wrapper (using the fix from our fork) so that
derpers will stop closing connections too aggressively.
Updates #5921
Signed-off-by: Mihai Parparita <mihai@tailscale.com>
If the wgcfg.Config is specified with network logging arguments,
then Userspace.Reconfig starts up an asynchronous network logger,
which is shutdown either upon Userspace.Close or when Userspace.Reconfig
is called again without network logging or route arguments.
Signed-off-by: Joe Tsai <joetsai@digital-static.net>
When Tailscale is installed via Homebrew, `/usr/local/bin/tailscaled`
is a symlink to the actual binary.
Now when `tailscaled install-system-daemon` runs, it will not attempt
to overwrite that symlink if it already points to the tailscaled binary.
However, if executed binary and the link target differ, the path will
he overwritten - this can happen when a user decides to replace
Homebrew-installed tailscaled with a one compiled from source code.
Fixes#5353
Signed-off-by: Anton Tolchanov <anton@tailscale.com>
If Wrapper.StatisticsEnable is enabled,
then per-connection counters are maintained.
If enabled, Wrapper.StatisticsExtract must be periodically called
otherwise there is unbounded memory growth.
Signed-off-by: Joe Tsai <joetsai@digital-static.net>
Most visible when using tsnet.Server, but could have resulted in dropped
messages in a few other places too.
Fixes#5743
Signed-off-by: Mihai Parparita <mihai@tailscale.com>
I added new functions to winutil to obtain the state of a service and all
its depedencies, serialize them to JSON, and write them to a Logf.
When tstun.New returns a wrapped ERROR_DEVICE_NOT_AVAILABLE, we know that wintun
installation failed. We then log the service graph rooted at "NetSetupSvc".
We are interested in that specific service because network devices will not
install if that service is not running.
Updates https://github.com/tailscale/tailscale/issues/5531
Signed-off-by: Aaron Klotz <aaron@tailscale.com>
* and move goroutine scrubbing code to its own package for reuse
* bump capver to 45
Change-Id: I9b4dfa5af44d2ecada6cc044cd1b5674ee427575
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
Personal preference (so it's obvious it's not a bool flag), but it
also matches the --state= before it.
Bonus: stop allowing PORT to sneak in extra flags to be passed as
their own arguments, as $FOO and ${FOO} expand differently. (${FOO} is
required to concat to strings)
Change-Id: I994626a5663fe0948116b46a971e5eb2c4023216
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
ipnserver previously had support for a Windows-only environment
variable mechanism that further only worked when Windows was running
as a service, not from a console.
But we want it to work from tailscaed too, and we want it to work on
macOS and Synology. So move it to envknob, now that envknob can change
values at runtime post-init.
A future change will wire this up for more platforms, and do something
more for CLI flags like --port, which the bug was originally about.
Updates #5114
Change-Id: I9fd69a9a91bb0f308fc264d4a6c33e0cbe352d71
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
The io/ioutil package has been deprecated as of Go 1.16 [1]. This commit
replaces the existing io/ioutil functions with their new definitions in
io and os packages.
Reference: https://golang.org/doc/go1.16#ioutil
Signed-off-by: Eng Zer Jun <engzerjun@gmail.com>
As noted in #5617, our documented method of blocking log.tailscale.io
DNS no longer works due to bootstrap DNS.
Instead, provide an explicit flag (--no-logs-no-support) and/or env
variable (TS_NO_LOGS_NO_SUPPORT=true) to explicitly disable logcatcher
uploads. It also sets a bit on Hostinfo to say that the node is in that
mode so we can end any support tickets from such nodes more quickly.
This does not yet provide an easy mechanism for users on some
platforms (such as Windows, macOS, Synology) to set flags/env. On
Linux you'd used /etc/default/tailscaled typically. Making it easier
to set flags for other platforms is tracked in #5114.
Fixes#5617Fixestailscale/corp#1475
Change-Id: I72404e1789f9e56ec47f9b7021b44c025f7a373a
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
NextDNS is unique in that users create accounts and then get
user-specific DNS IPs & DoH URLs.
For DoH, the customer ID is in the URL path.
For IPv6, the IP address includes the customer ID in the lower bits.
For IPv4, there's a fragile "IP linking" mechanism to associate your
public IPv4 with an assigned NextDNS IPv4 and that tuple maps to your
customer ID.
We don't use the IP linking mechanism.
Instead, NextDNS is DoH-only. Which means using NextDNS necessarily
shunts all DNS traffic through 100.100.100.100 (programming the OS to
use 100.100.100.100 as the global resolver) because operating systems
can't usually do DoH themselves.
Once it's in Tailscale's DoH client, we then connect out to the known
NextDNS IPv4/IPv6 anycast addresses.
If the control plane sends the client a NextDNS IPv6 address, we then
map it to the corresponding NextDNS DoH with the same client ID, and
we dial that DoH server using the combination of v4/v6 anycast IPs.
Updates #2452
Change-Id: I3439d798d21d5fc9df5a2701839910f5bef85463
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
This is entirely optional (i.e. failing in this code is non-fatal) and
only enabled on Linux for now. Additionally, this new behaviour can be
disabled by setting the TS_DEBUG_DISABLE_AF_PACKET environment variable.
Updates #3824
Replaces #5474
Co-authored-by: Andrew Dunham <andrew@du.nham.ca>
Signed-off-by: David Anderson <danderson@tailscale.com>
This lets the control plane can make HTTP requests to nodes.
Then we can use this for future things rather than slapping more stuff
into MapResponse, etc.
Change-Id: Ic802078c50d33653ae1f79d1e5257e7ade4408fd
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
This works around the 2.3s delay in short name lookups when SNR is
enabled.
C:\Windows\System32\drivers\etc\hosts file. We only add known hosts that
match the search domains, and we populate the list in order of
Search Domains so that our matching algorithm mimics what Windows would
otherwise do itself if SNR was off.
Updates #1659
Signed-off-by: Maisem Ali <maisem@tailscale.com>
Apparently OpenBSD can forward packets with manual configuration,
https://github.com/tailscale/tailscale/issues/2498#issuecomment-1114216999
But this makes it work by default. People doing things by hand can
set TS_DEBUG_WRAP_NETSTACK=0 in the environment.
Change-Id: Iee5f32252f83af2baa0ebbe3f20ce9fec5f29e96
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
Switch deephash to use sha256x.Hash.
We add sha256x.HashString to efficiently hash a string.
It uses unsafe under the hood to convert a string to a []byte.
We also modify sha256x.Hash to export the underlying hash.Hash
for testing purposes so that we can intercept all hash.Hash calls.
Performance:
name old time/op new time/op delta
Hash-24 19.8µs ± 1% 19.2µs ± 1% -3.01% (p=0.000 n=10+10)
HashPacketFilter-24 2.61µs ± 0% 2.53µs ± 1% -3.01% (p=0.000 n=8+10)
HashMapAcyclic-24 31.3µs ± 1% 29.8µs ± 0% -4.80% (p=0.000 n=10+9)
TailcfgNode-24 1.83µs ± 1% 1.82µs ± 2% ~ (p=0.305 n=10+10)
HashArray-24 344ns ± 2% 323ns ± 1% -6.02% (p=0.000 n=9+10)
The performance gains is not as dramatic as sha256x over sha256 due to:
1. most of the hashing already occurring through the direct memory hashing logic, and
2. what does not go through direct memory hashing is slowed down by reflect.
Signed-off-by: Joe Tsai <joetsai@digital-static.net>
Following the pattern elsewhere, we create a new tka-specific types package for the types
that need to couple between the serialized structure types, and tka.
Signed-off-by: Tom DNetto <tom@tailscale.com>
- A network-lock key is generated if it doesn't already exist, and stored in the StateStore. The public component is communicated to control during registration.
- If TKA state exists on the filesystem, a tailnet key authority is initialized (but nothing is done with it for now).
Signed-off-by: Tom DNetto <tom@tailscale.com>
This adds the inverse to CapabilityFileSharingSend so that senders can
identify who they can Taildrop to.
Updates #2101
Signed-off-by: Maisem Ali <maisem@tailscale.com>
3f686688a6 regressed the Windows beFirewallKillswitch code,
preventing the /firewall subprocess from running.
Fixestailscale/corp#6063
Change-Id: Ibd105759e5fecfeffc54f587f8ddcd0f1cbc4dca
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
And rewrite cloud detection to try to do only zero or one metadata
discovery request for all clouds, only doing a first (or second) as
confidence increases. Work remains for Windows, but a start.
And add Cloud to tailcfg.Hostinfo, which helped with testing using
"tailcfg debug hostinfo".
Updates #4983 (Linux only)
Updates #4984
Change-Id: Ib03337089122ce0cb38c34f724ba4b4812bc614e
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
And remove the GCP special-casing from ipn/ipnlocal; do it only in the
forwarder for *.internal.
Fixes#4980Fixes#4981
Change-Id: I5c481e96d91f3d51d274a80fbd37c38f16dfa5cb
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
This does three things:
* If you're on GCP, it adds a *.internal DNS split route to the
metadata server, so we never break GCP DNS names. This lets people
have some Tailscale nodes on GCP and some not (e.g. laptops at home)
without having to add a Tailnet-wide *.internal DNS route.
If you already have such a route, though, it won't overwrite it.
* If the 100.100.100.100 DNS forwarder has nowhere to forward to,
it forwards it to the GCP metadata IP, which forwards to 8.8.8.8.
This means there are never errNoUpstreams ("upstream nameservers not set")
errors on GCP due to e.g. mangled /etc/resolv.conf (GCP default VMs
don't have systemd-resolved, so it's likely a DNS supremacy fight)
* makes the DNS fallback mechanism use the GCP metadata IP as a
fallback before our hosted HTTP-based fallbacks
I created a default GCP VM from their web wizard. It has no
systemd-resolved.
I then made its /etc/resolv.conf be empty and deleted its GCP
hostnames in /etc/hosts.
I then logged in to a tailnet with no global DNS settings.
With this, tailscaled writes /etc/resolv.conf (direct mode, as no
systemd-resolved) and sets it to 100.100.100.100, which then has
regular DNS via the metadata IP and *.internal DNS via the metadata IP
as well. If the tailnet configures explicit DNS servers, those are used
instead, except for *.internal.
This also adds a new util/cloudenv package based on version/distro
where the cloud type is only detected once. We'll likely expand it in
the future for other clouds, doing variants of this change for other
popular cloud environments.
Fixes#4911
RELNOTES=Google Cloud DNS improvements
Change-Id: I19f3c2075983669b2b2c0f29a548da8de373c7cf
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
We weren't wiring up netstack.Impl to the LocalBackend in some cases
on Windows. This fixes Windows 7 when run as a service.
Updates #4750 (fixes after pull in to corp repo)
Change-Id: I9ce51b797710f2bedfa90545776b7628c7528e99
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
We can't do Noise-over-HTTP in Wasm/JS (because we don't have bidirectional
communication), but we should be able to do it over WebSockets. Reuses
derp WebSocket support that allows us to turn a WebSocket connection
into a net.Conn.
Updates #3157
Signed-off-by: Mihai Parparita <mihai@tailscale.com>
AFAICT this isn't documented on MSDN, but based on the issue referenced below,
NRPT rules are not working when a rule specifies > 50 domains.
This patch modifies our NRPT rule generator to split the list of domains
into chunks as necessary, and write a separate rule for each chunk.
For compatibility reasons, we continue to use the hard-coded rule ID, but
as additional rules are required, we generate new GUIDs. Those GUIDs are
stored under the Tailscale registry path so that we know which rules are ours.
I made some changes to winutils to add additional helper functions in support
of both the code and its test: I added additional registry accessors, and also
moved some token accessors from paths to util/winutil.
Fixes https://github.com/tailscale/coral/issues/63
Signed-off-by: Aaron Klotz <aaron@tailscale.com>
I wrote this code way back at the beginning of my tenure at Tailscale when we
had concerns about needing to restore deleted machine keys from backups.
We never ended up using this functionality, and the code is now getting in the
way, so we might as well remove it.
Signed-off-by: Aaron Klotz <aaron@tailscale.com>
Enables the behavior described in the statepath flag, where if only
statedir is passed, then state is statedir/tailscaled.state.
Signed-off-by: James Tucker <james@tailscale.com>
Once a stop request is received and the service updates its status to `svc.StopPending`,
it should continue running *until the shutdown sequence is complete*, and then
return out of `(*ipnService).Execute`, which automatically sends a `svc.Stopped`
notification to Windows.
To make this happen, I changed the loop so that it runs until `doneCh` is
closed, and then returns. I also removed a spurious `svc.StopPending` notification
that the Windows Service Control Manager might be interpreting as a request for
more time to shut down.
Finally, I added some optional logging that sends a record of service notifications
to the Windows event log, allowing us to more easily correlate with any Service
Control Manager errors that are sent to the same log.
Change-Id: I5b596122e5e89c4c655fe747a612a52cb4e8f1e0
Signed-off-by: Aaron Klotz <aaron@tailscale.com>
Well, goimports actually (which adds the normal import grouping order we do)
Change-Id: I0ce1b1c03185f3741aad67c14a7ec91a838de389
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
The connections returned from SystemDial are automatically closed when
there is a major link change.
Also plumb through the dialer to the noise client so that connections
are auto-reset when moving from cellular to WiFi etc.
Updates #3363
Signed-off-by: Maisem Ali <maisem@tailscale.com>
No CLI support yet. Just the curl'able version if you know the peerapi
port. (like via a TSMP ping)
Updates #306
Change-Id: I0662ba6530f7ab58d0ddb24e3664167fcd1c4bcf
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
I've done this a handful of times in the past and again today.
Time to make it a supported thing for the future.
Used while debugging tailscale/corp#4559 (macsys CLI issues)
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
This reverts commit 8d6793fd70.
Reason: breaks Android build (cgo/pthreads addition)
We can try again next cycle.
Change-Id: I5e7e1730a8bf399a8acfce546a6d22e11fb835d5
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
Attempt to load the xt_mark kernel module when it is not present. If the
load fails, log error information.
It may be tempting to promote this failure to an error once it has been
in use for some time, so as to avoid reaching an error with the iptables
invocation, however, there are conditions under which the two stages may
disagree - this change adds more useful breadcrumbs.
Example new output from tailscaled running under my WSL2:
```
router: ensure module xt_mark: "/usr/sbin/modprobe xt_mark" failed: exit status 1; modprobe: FATAL: Module xt_mark not found in directory /lib/modules/5.10.43.3-microsoft-standard-WSL2
```
Background:
There are two places to lookup modules, one is `/proc/modules` "old",
the other is `/sys/module/` "new".
There was query_modules(2) in linux <2.6, alas, it is gone.
In a docker container in the default configuration, you would get
/proc/modules and /sys/module/ both populated. lsmod may work file,
modprobe will fail with EPERM at `finit_module()` for an unpriviliged
container.
In a priviliged container the load may *succeed*, if some conditions are
met. This condition should be avoided, but the code landing in this
change does not attempt to avoid this scenario as it is both difficult
to detect, and has a very uncertain impact.
In an nspawn container `/proc/modules` is populated, but `/sys/module`
does not exist. Modern `lsmod` versions will fail to gather most module
information, without sysfs being populated with module information.
In WSL2 modules are likely missing, as the in-use kernel typically is
not provided by the distribution filesystem, and WSL does not mount in a
module filesystem of its own. Notably the WSL2 kernel supports iptables
marks without listing the xt_mark module in /sys/module, and
/proc/modules is empty.
On a recent kernel, we can ask the capabilities system about SYS_MODULE,
that will help to disambiguate between the non-privileged container case
and just being root. On older kernels these calls may fail.
Update #4329
Signed-off-by: James Tucker <james@tailscale.com>
Remove the weird netstack -> tailssh dependency and instead have tailssh
register itself with ipnlocal when linked.
This makes tailssh.server a singleton, so we can have a global map of
all sessions.
Updates #3802
Change-Id: Iad5caec3a26a33011796878ab66b8e7b49339f29
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
This extracts DOH mapping of known public DNS providers in
forwarder.go into its own package, to be consumed by other repos
Signed-off-by: Jenny Zhang <jz@tailscale.com>
Usage of userspace-networking is increasing, and the aggressive GC
tuning causes a significant reduction in performance in that mode.
Signed-off-by: James Tucker <james@tailscale.com>
In tracking down issue #4144 and reading through the netstack code in
detail, I discovered that the packet buf Clone path did not reset the
packetbuf it was getting from the sync.Pool. The fix was sent upstream
https://github.com/google/gvisor/pull/7385, and this bump pulls that in.
At this time there is no known path that this fixes, however at the time
of upstream submission this reset at least one field that could lead to
incorrect packet routing if exercised, a situation that could therefore
lead to an information leak.
Signed-off-by: James Tucker <james@tailscale.com>
In addition an envknob (TS_DEBUG_NETSTACK_LEAK_MODE) now provides access
to set leak tracking to more useful values.
Fixes#4309
Signed-off-by: James Tucker <james@tailscale.com>
While we rearrange/upstream things.
gliderlabs/ssh is forked into tempfork from our prior fork
at be8b7add40
x/crypto/ssh OTOH is forked at
https://github.com/tailscale/golang-x-crypto because it was gnarlier
to vendor with various internal packages, etc.
Its git history shows where it starts (2c7772ba30643b7a2026cbea938420dce7c6384d).
Updates #3802
Change-Id: I546e5cdf831cfc030a6c42557c0ad2c58766c65f
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
The best flag to use on Win7 and Win8.0 is deprecated in Win8.1, so we resolve
the flag depending on OS version info.
Fixes https://github.com/tailscale/tailscale/issues/4201
Signed-off-by: Aaron Klotz <aaron@tailscale.com>
Due to a bug in Go (golang/go#51778), cmd/go doesn't warn about your
Go version being older than the go.mod's declared Go version in that
case that package loading fails before the build starts, such as when
you use packages that are only in the current version of Go, like our
use of net/netip.
This change works around that Go bug by adding build tags and a
pre-Go1.18-only file that will cause Go 1.17 and earlier to fail like:
$ ~/sdk/go1.17/bin/go install ./cmd/tailscaled
# tailscale.com/cmd/tailscaled
./required_version.go:11:2: undefined: you_need_Go_1_18_to_compile_Tailscale
note: module requires Go 1.18
Change-Id: I39f5820de646703e19dde448dd86a7022252f75c
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
The docs say:
Note that while correct uses of TryLock do exist, they are rare,
and use of TryLock is often a sign of a deeper problem in a particular use of mutexes.
Rare code! Or bad code! Who can tell!
Signed-off-by: Josh Bleecher Snyder <josh@tailscale.com>
It includes a fix to allow us to use Go 1.18.
We can now remove our Tailscale-only build tags.
Signed-off-by: Josh Bleecher Snyder <josh@tailscale.com>
The certstore code is impacted by golang/go#51726.
The Tailscale Go toolchain fork contains a temporary workaround,
so it can compile it. Once the upstream toolchain can compile certstore,
presumably in Go 1.18.1, we can revert this change.
Note that depaware runs with the upstream toolchain.
Signed-off-by: Josh Bleecher Snyder <josh@tailscale.com>
Still not sure the exact rules of how/when/who's supposed to set
these, but this works for now on making them match. Baby steps.
Will research more and adjust later.
Updates #4146 (but not enough to fix it, something's still wrong)
Updates #3802
Change-Id: I496d8cd7e31d45fe9ede88fc8894f35dc096de67
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
One of the current few steps to run Tailscale on gokrazy is to
specify the --tun=userspace-networking flag:
https://gokrazy.org/userguide/install/tailscale/
Instead, make it the default for now. Later we can change the
default to kernel mode if available and fall back to userspace
mode like Synology, once #391 is done.
Likewise, set default paths for Gokrazy, as its filesystem hierarchy
is not the Linux standard one. Instead, use the conventional paths as
documented at https://gokrazy.org/userguide/install/tailscale/.
Updates #1866
RELNOTE=default to userspace-networking mode on gokrazy
Change-Id: I3766159a294738597b4b30629d2860312dbb7609
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
If it's in a non-standard table, as it is on Unifi UDM Pro, apparently.
Updates #4038 (probably fixes, but don't have hardware to verify)
Change-Id: I2cb9a098d8bb07d1a97a6045b686aca31763a937
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
Also move KubeStore and MemStore into their own package.
RELNOTE: tsnet now supports providing a custom ipn.StateStore.
Signed-off-by: Maisem Ali <maisem@tailscale.com>
Turns out we're pretty good already at init-time work in tailscaled.
The regexp/syntax shows up but it's hard to get rid of that; zstd even
uses regexp. *shrug*
Change-Id: I856aca056dcb7489f5fc22ef07f55f34ddf19bd6
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
For ssh and maybe windows service babysitter later.
Updates #3802
Change-Id: I7492b98df98971b3fb72d148ba92c2276cca491f
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
For local dev testing initially. Product-wise, it'll probably only be
workable on the two unsandboxed builds.
Updates #3802
Change-Id: Ic352f966e7fb29aff897217d79b383131bf3f92b
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
Still largely incomplete, but in a better home now.
Updates #3802
Change-Id: I46c5ffdeb12e306879af801b06266839157bc624
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
I was about to add a third copy, so unify them now instead.
Change-Id: I3b93896aa1249b1250a6b1df4829d57717f2311a
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
This patch adds new functions to be used when accessing system policies,
and revises callers to use the new functions. They first attempt the new
registry path for policies, and if that fails, attempt to fall back to the
legacy path.
We keep non-policy variants of these functions because we should be able to
retain the ability to read settings from locations that are not exposed to
sysadmins for group policy edits.
The remaining changes will be done in corp.
Updates https://github.com/tailscale/tailscale/issues/3584
Signed-off-by: Aaron Klotz <aaron@tailscale.com>
Now that Go 1.17 has module graph pruning
(https://go.dev/doc/go1.17#go-command), we should be able to use
upstream netstack without breaking our private repo's build
that then depends on the tailscale.com Go module.
This is that experiment.
Updates #1518 (the original bug to break out netstack to own module)
Updates #2642 (this updates netstack, but doesn't remove workaround)
Change-Id: I27a252c74a517053462e5250db09f379de8ac8ff
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
Disabled by default.
To use, run tailscaled with:
TS_SSH_ALLOW_LOGIN=you@bar.com
And enable with:
$ TAILSCALE_USE_WIP_CODE=true tailscale up --ssh=true
Then ssh [any-user]@[your-tailscale-ip] for a root bash shell.
(both the "root" and "bash" part are temporary)
Updates #3802
Change-Id: I268f8c3c95c8eed5f3231d712a5dc89615a406f0
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
A new package can also later record/report which knobs are checked and
set. It also makes the code cleaner & easier to grep for env knobs.
Change-Id: Id8a123ab7539f1fadbd27e0cbeac79c2e4f09751
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
Treat UDP send EPERM errors as a lost UDP packet, not something super
fatal. That's just the Linux firewall preventing it from going out.
And add a leaf package net/neterror for that (and future) policy that
all three packages can share, with tests.
Updates #3619
Change-Id: Ibdb838c43ee9efe70f4f25f7fc7fdf4607ba9c1d
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
This is for use by the Windows GUI client to log via when an
exit node is in use, so the logs don't go out via the exit node and
instead go directly, like tailscaled's. The dialer tried to do that
in the unprivileged GUI by binding to a specific interface, but the
"Internet Kill Switch" installed by tailscaled for exit nodes
precludes that from working and instead the GUI fails to dial out.
So, go through tailscaled (with a CONNECT request) instead.
Fixestailscale/corp#3169
Change-Id: I17a8efdc1d4b8fed53a29d1c19995592b651b215
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
This moves the Windows-only initialization of the filelogger into
logpolicy. Previously we only did it when babysitting the tailscaled
subprocess, but this meant that log messages from the service itself
never made it to disk. Examples that weren't logged to disk:
* logtail unable to dial out,
* DNS flush messages from the service
* svc.ChangeRequest messages (#3581)
This is basically the same fix as #3571 but staying in the Logf type,
and avoiding build-tagged file (which wasn't quite a goal, but
happened and seemed nice)
Fixes#3570
Co-authored-by: Aaron Klotz <aaron@tailscale.com>
Change-Id: Iacd80c4720b7218365ec80ae143339d030842702
I broke it in 1.17.x sometime while rewiring some logs stuff,
mostly in 0653efb092 (but with a handful
of logs-related changes around that time)
Fixestailscale/corp#3265
Change-Id: Icb5c07412dc6d55f1d9244c5d0b51dceca6a7e34
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
This is enough to handle the DNS queries as generated by Go's
net package (which our HTTP/SOCKS client uses), and the responses
generated by the ExitDNS DoH server.
This isn't yet suitable for putting on 100.100.100.100 where a number
of different DNS clients would hit it, as this doesn't yet do
EDNS0. It might work, but it's untested and likely incomplete.
Likewise, this doesn't handle anything about truncation, as the
exchanges are entirely in memory between Go or DoH. That would also
need to be handled later, if/when it's hooked up to 100.100.100.100.
Updates #3507
Change-Id: I1736b0ad31eea85ea853b310c52c5e6bf65c6e2a
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
The caller of func run said:
// No need to log; the func already did
But that wasn't true. Some return paths didn't log.
So instead, return rich errors and have func main do the logging,
so we can't miss anything in the future.
Prior to this, safesocket.Listen for instance was causing tailscaled
to os.Exit(1) on failure without any clue as to why.
Change-Id: I9d71cc4d73d0fed4aa1b1902cae199f584f25793
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
To make ExitDNS cheaper.
Might not finish client-side support in December before 1.20, but at
least server support can start rolling out ahead of clients being
ready for it.
Tested with curl against peerapi.
Updates #1713
Change-Id: I676fed5fb1aef67e78c542a3bc93bddd04dd11fe
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
And simplify, unexport some tsdial/netstack stuff in the the process.
Fixes#3475
Change-Id: I186a5a5cbd8958e25c075b4676f7f6e70f3ff76e
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
This starts to refactor tsdial.Dialer's name resolution to have
different stages: in-memory MagicDNS vs system resolution. A future
change will plug in ExitDNS resolution.
This also plumbs a Dialer into netstack and unexports the dnsMap
internals.
And it removes some of the async AddNetworkMapCallback usage and
replaces it with synchronous updates of the Dialer's netmap
from LocalBackend, since the LocalBackend has the Dialer too.
Updates #3475
Change-Id: Idcb7b1169878c74f0522f5151031ccbc49fe4cb4
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
In prep for moving stuff out of LocalBackend.
Change-Id: I9725aa9c3ebc7275f8c40e040b326483c0340127
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
Not done yet, but this move more of the outbound dial special casing
from random packages into tsdial, which aspires to be the one unified
place for all outbound dialing shenanigans.
Then this plumbs it all around, so everybody is ultimately
holding on to the same dialer.
As of this commit, macOS/iOS using an exit node should be able to
reach to the exit node's DoH DNS proxy over peerapi, doing the sockopt
to stay within the Network Extension.
A number of steps remain, including but limited to:
* move a bunch more random dialing stuff
* make netstack-mode tailscaled be able to use exit node's DNS proxy,
teaching tsdial's resolver to use it when an exit node is in use.
Updates #1713
Change-Id: I1e8ee378f125421c2b816f47bc2c6d913ddcd2f5
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
For now this just deletes the net/socks5/tssocks implementation (and
the DNSMap stuff from wgengine/netstack) and moves it into net/tsdial.
Then initialize a Dialer early in tailscaled, currently only use for the
outbound and SOCKS5 proxies. It will be plumbed more later. Notably, it
needs to get down into the DNS forwarder for exit node DNS forwading
in netstack mode. But it will also absorb all the peerapi setsockopt
and netns Dial and tlsdial complexity too.
Updates #1713
Change-Id: Ibc6d56ae21a22655b2fa1002d8fc3f2b2ae8b6df
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
When this happens, it is incredibly noisy in the logs.
It accounts for about a third of all remaining
"unexpected" log lines from a recent investigation.
It's not clear that we know how to fix this,
we have a functioning workaround,
and we now have a (cheap and efficient) metric for this
that we can use for measurements.
So reduce the logging to approximately once per minute.
Signed-off-by: Josh Bleecher Snyder <josh@tailscale.com>
wgengine/wgcfg: introduce wgcfg.NewDevice helper to disable roaming
at all call sites (one real plus several tests).
Fixestailscale/corp#3016.
Signed-off-by: David Anderson <danderson@tailscale.com>
Signed-off-by: Josh Bleecher Snyder <josh@tailscale.com>
And annotate magicsock as a start.
And add localapi and debug handlers with the Prometheus-format
exporter.
Updates #3307
Change-Id: I47c5d535fe54424741df143d052760387248f8d3
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
More work towards removing the massive ipnserver.Run and ipnserver.Options
and making composable pieces.
Work remains. (The getEngine retry loop on Windows complicates things.)
For now some duplicate code exists. Once the Windows side is fixed
to either not need the retry loop or to move the retry loop into a
custom wgengine.Engine wrapper, then we can unify tailscaled_windows.go
too.
Change-Id: If84d16e3cd15b54ead3c3bb301f27ae78d055f80
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
github.com/go-multierror/multierror served us well.
But we need a few feature from it (implement Is),
and it's not worth maintaining a fork of such a small module.
Instead, I did a clean room implementation inspired by its API.
Signed-off-by: Josh Bleecher Snyder <josh@tailscale.com>
Using temporary netlink fork in github.com/tailscale/netlink until we
get the necessary changes upstream in either vishvananda/netlink
or jsimonetti/rtnetlink.
Updates #391
Change-Id: I6e1de96cf0750ccba53dabff670aca0c56dffb7c
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
Even if not in use. We plan to use it for more stuff later.
(not for iOS or macOS-GUIs yet; only tailscaled)
Change-Id: Idaef719d2a009be6a39f158fd8f57f8cca68e0ee
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
Temporary measure until we switch to Go 1.18.
$ go run ./cmd/tailscale version
1.17.0-date.20211022
go version: go1.17
Updates #81
Change-Id: Ic82ebffa5f46789089e5fb9810b3f29e36a47f1a
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
utils/winutil/vss contains just enough COM wrapping to query the Volume Shadow Copy service for snapshots.
WalkSnapshotsForLegacyStateDir is the friendlier interface that adds awareness of our actual use case,
mapping the snapshots and locating our legacy state directory.
Updates #3011
Signed-off-by: Aaron Klotz <aaron@tailscale.com>
From https://github.com/tailscale/tailscale/pull/1919 with
edits by bradfitz@.
This change introduces a new storage provider for the state file. It
allows users to leverage AWS SSM parameter store natively within
tailscaled, like:
$ tailscaled --state=arn:aws:ssm:eu-west-1:123456789:parameter/foo
Known limitations:
- it is not currently possible to specific a custom KMS key ID
RELNOTE=tailscaled on Linux supports using AWS SSM for state
Edits-By: Brad Fitzpatrick <bradfitz@tailscale.com>
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
Signed-off-by: Maxime VISONNEAU <maxime.visonneau@gmail.com>
This feature wasn't working until I realized that we also need to opt into
the events. MSDN wasn't so generous as to make this easy to deduce.
Updates #2956
Signed-off-by: Aaron Klotz <aaron@tailscale.com>
The old name invited confusion:
* is this the HTTP proxy to use ourselves? (no, that's
via an environment variable, per proxy conventions)
* is this for LetsEncrypt https-to-localhost-http
proxying? (no, that'll come later)
So rename to super verbose --outbound-http-proxy-listen
before the 1.16.0 release to make it clear what it is.
It listens (serves) and it's for outbound, not inbound.
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
For the service, all we need to do is handle the `svc.SessionChange` command.
Upon receipt of a `windows.WTS_SESSION_UNLOCK` event, we fire off a goroutine to flush the DNS cache.
(Windows expects responses to service requests to be quick, so we don't want to do that synchronously.)
This is gated on an integral registry value named `FlushDNSOnSessionUnlock`,
whose value we obtain during service initialization.
(See [this link](https://docs.microsoft.com/en-us/windows/win32/api/winsvc/nc-winsvc-lphandler_function_ex) for information re: handling `SERVICE_CONTROL_SESSIONCHANGE`.)
Fixes#2956
Signed-off-by: Aaron Klotz <aaron@tailscale.com>
Brad Fitzpatrick